1) Field of the Invention
This invention relates to a tandem color image formation apparatus and a tandem color image formation method.
2) Description of the Related Art
Conventionally, tandem color image formation apparatuses each of which has a plurality of image processing sections have been widely spread. One example of the tandem color image formation apparatus of this type will be explained with reference to FIGS. 7 to 10. FIG. 7 is a schematic diagram which shows the overall configuration of a color image formation apparatus. FIG. 8 is a perspective view which shows apart of the color image formation apparatus. FIG. 9 is an explanatory view which shows alignment marks transferred onto a conveyor belt and sensors which detect the marks. FIG. 10 is an explanatory view which shows density adjustment marks transferred onto the conveyor belt and a sensor which detects the marks.
This color image formation apparatus includes four image processing sections 1Y, 1M, 1C and 1K which form images of different colors (yellow Y, magenta M, cyan C and black K) and a conveyor belt 3 which transfers a sheet 2 onto which a formed image is transferred. The conveyor belt 3 is an endless belt which is supported by a driving roller 4 and a driven roller 5 and which is driven to rotate. The four image processing sections 1Y, 1M, 1C and 1K are aligned along the moving direction of this conveyor belt 3.
The four image processing sections 1Y, 1M, 1C and 1K form images of yellow Y, magenta M, cyan C and black K, respectively, and are equal in structure. Therefore, only the image processing section 1Y will be concretely explained hereafter while the other image processing sections 1M, 1C and 1K are shown only in FIG. 7 and FIG. 8 by denoting the constituent elements of the image processing sections 1M, 1C and 1K by reference symbols replacing the corresponding reference symbols for those of the image processing section 1Y.
A paper feed tray 6 which contains sheets 2 is arranged below the conveyor belt 3. In forming an image, the sheets 2 contained in the paper feed tray 6 starting at the uppermost sheet 6 are sequentially fed out and attached to the conveyor belt 3 by electrostatic chucking. The sheets 2 attached to the conveyor belt 3 are transferred to the first image processing section 1Y in which a yellow toner image is transferred onto the sheets 6, respectively.
The image processing section 1Y consists of a photosensitive drum 7Y serving as an image carrier, a charger 8Y disposed around the photosensitive drum 7Y, an exposure device 9, a developer 10Y, a photosensitive cleaner 11Y, a transfer device 12Y and the like. The exposure device 9 is employed by not only the image processing section 1Y but also the other image processing sections 1M, 1C and 1K. A yellow image laser beam LY is applied to the photosensitive drum 7Y, a magenta image laser beam LM is applied to a photosensitive drum 7M, a cyan image laser beam LC is applied to a photosensitive drum 7C and a black image laser beam LK is applied to a photosensitive drum 7K.
Each of the sheets 2 conveyed by the conveyor belt 3 onto which the yellow toner image is transferred, is then subjected to the transfer of a magenta toner image in the image processing section 1M, the transfer of a cyan toner image in the image processing section 1C and the transfer of a black toner image in the image processing section 1K. The sheet 6 onto which these images are transferred is peeled off from the conveyor belt 3, fed into a fixing device 13 in which a toner image fixing processing is conducted to the sheet 6.
Three sensors 14, 15 and 16 which are arranged to face the front surface of the conveyor belt 3 in a direction (main scan direction) orthogonal to the moving direction (sub-scan direction) of the conveyor belt 3, below the conveyor belt 3 and near the driven roller 5. These sensors 14, 15 and 16 are used to detect alignment marks 17 formed by the image processing sections 1Y, 1M, 1C and 1K and transferred onto the conveyor belt 3. Among them, the sensor 14 is used to detect density adjustment marks 18 (see FIG. 10) formed by the image processing sections 1Y, 1M, 1C and 1K and transferred onto the conveyor belt 3.
A belt cleaner 19 which cleans the alignment marks 17 and the density adjustment marks 18 transferred onto the conveyor belt 3, is provided slightly downstream of the sensors 14, 15 and 16 along the moving direction of the conveyor belt 3.
As shown in FIG. 9, the alignment marks 17 are formed at positions opposed to the sensors 14, 15 and 16, respectively, on the conveyor belt 3. Each alignment mark 17 consists of a line mark (lateral line mark) parallel to the main scan direction and a line mark (inclined mark) inclined relative to this lateral line mark. The sensors 14, 15 and 16 read the alignment marks 17, respectively. A control section, not shown, which includes a main CPU performs an arithmetic operation for an image slippage quantity and that for a correction quantity to eliminate the slippage and issues a correction execution instruction for each color based on the read result. It is thereby possible to adjust the following five positional slippages, 1 a sub-scan registration slippage caused by the error of the axial distance among the photosensitive drums 7Y, 7M, 7C and 7K provided in the image processing sections 1Y, 1M, 1C and 1K, respectively, 2 an inclination slippage caused by the uneven inclinations of the photosensitive drums 7Y, 7M, 7C and 7K provided in the image processing sections 1Y, 1M, 1C and 1K, respectively in the main scan direction, 3 a main scan resist slippage caused by the slippage of respective image write positions, 4 a scaling slippage caused by the different lengths of scanning lines for the four colors, respectively, and 5 a scaling error deviation slippage caused by a partial error in the scaling of the main scan direction. If the positional slippages 1 to 4 are to be adjusted, it suffices to employ only the two sensors 14 and 16.
As shown in FIG. 10, the density adjustment marks 18 are formed on positions facing the sensor 14 on the conveyor belt 3 and formed as gradation images by changing densities for the respective colors, respectively. The sensor 14 reads the density adjustment marks 18. The control section, not shown, performs an arithmetic operation for density and that for a correction quantity for the density and issues a correction execution instruction for each color, whereby the density of a resultant image can be optimally controlled.
Conventionally, the density adjustment mark 18 for adjusting the density of the image of each color is detected by the sensor 14 which detects the alignment mark 17 for aligning the images of the respective colors to one another. Concrete procedures for the detection of the alignment marks 17 and the density adjustment marks 18 are as follows.
Alignment marks 17 are first formed, transferred onto the conveyor belt 3, detected by the sensors 14, 15 and 16, respectively, and cleaned by the belt cleaner 19 after being detected. After cleaning, density adjustment marks 18 are formed, transferred onto the conveyor belt 3, detected by the sensor 14 and cleaned by the belt cleaner 19 after being detected.
That is, after the completion of the formation, transfer, detection and cleaning of the alignment marks 17, the formation, transfer, detection and cleaning of the density adjustment marks 18 start. As a result, a lot of time is required until operations for the alignment of the images of the respective colors and the density adjustment thereof are finished, disadvantageously deteriorating work efficiency for image formation.
It is an object of the present invention to reduce time required for the alignment and density adjustment of images of respective colors and to enhance work efficiency for image formation.
According to one aspect of the present invention, a color image formation apparatus comprises, an endless belt which is driven to rotate, a plurality of image processing sections which are arranged along a moving direction of the endless belt and which form images of different colors, respectively, and a plurality of alignment sensors which are arranged in a direction orthogonal to the moving direction of the endless belt and each of which detects an alignment mark for each color formed by each of the image processing sections and transferred onto the endless belt, wherein the color image formation apparatus comprises a density adjustment sensor which is arranged at a position at which a detection area of the density adjustment sensor does not overlap detection areas of the alignment sensors in the direction orthogonal to the moving direction of the endless belt, and which detects a density adjustment mark transferred onto the endless belt, and wherein densities of the images formed by the image processing sections are adjusted corresponding to a detected result of the density adjustment sensor.
Accordingly, the alignment sensors which detect the alignment marks transferred onto the endless belt and the density adjustment sensor which detects the density adjustment marks transferred onto the endless belt are provided separately from each other. In addition, the alignment sensor and the density adjustment sensor are arranged so that the detection area of the density adjustment sensor does not overlap with those of the alignment sensors in the direction orthogonal to the moving direction of the endless belt. It is, therefore, possible to detect the alignment marks by the alignment sensors and the density adjustment marks by the density adjustment sensor in parallel. It is also possible to reduce time required until the alignment of images of respective colors performed based on detected results for the alignment marks and density adjustment of the images performed based on detected results for the density adjustment marks are finished. It is thereby possible to enhance work efficiency for image formation.
These and other objects, features and advantages of the present invention are specifically set forth in or will become apparent from the following detailed descriptions of the invention when read in conjunction with the accompanying drawings.